Transmittance-Variable Device

ABSTRACT

A transmittance-variable device is provided in the present application. The present application provides a transmittance-variable device, which can be applied to various applications without causing problems such as a crosstalk phenomenon, a rainbow phenomenon or a mirroring phenomenon, while having excellent transmittance-variable characteristics.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.17/270,090, filed Feb. 22, 2021, which is a national phase entry under35 U.S.C. § 371 of International Application No. PCT/KR2019/011380,filed Sep. 4, 2019, which claims priority from Korean Patent ApplicationNos. 10-2018-0105601 and 10-2018-0105597, filed on Sep. 4, 2018, thedisclosures of which are incorporated herein by reference in theirentirety.

TECHNICAL FIELD

The present application relates to a transmittance-variable device.

BACKGROUND ART

Devices that can vary transmittance with liquid crystal compounds andthe like are known. For example, in Patent Document 1, atransmittance-variable device using a so-called GH cell (guest hostcell) to which a liquid crystal host material and a dichroic dye guestare applied, is known.

The use of such devices has gradually expanded, and for example, thedevices may be used in wearable devices such as eyewear of glasses orsunglasses, and the like, mobile devices, devices for virtual reality(VR) or augmented reality (AR) or windows of vehicles, or appliancesthat are applied outdoors.

In the case of a device for adjusting the transmittance by applying aliquid crystal compound, polarized light above a certain level isbasically generated, where such a device causes problems such as acrosstalk phenomenon, a rainbow phenomenon or a mirroring phenomenon asthe reflected light by road surfaces or structures, buildings, and thelike has partially polarization characteristics depending on the useenvironments.

DISCLOSURE Technical Problem

The present application relates to a transmittance-variable device. Itis an object of the present application to provide atransmittance-variable device capable of being applied to variousapplications without causing problems such as a crosstalk phenomenon, arainbow phenomenon or a minoring phenomenon.

Technical Solution

The angle defined in this specification should be understood inconsideration of an error such as a manufacturing error or a variation.For example, in this specification, the term vertical, parallel,orthogonal or horizontal, and the like may mean substantially vertical,parallel, orthogonal or horizontal in a range that does not impair thepurpose and effect, and for example, in each case, it may include anerror within about ±10 degrees, an error within about ±5 degrees, anerror within about ±3 degrees, an error within about ±2 degrees, anerror within about ±1 degree or an error within about ±0.5 degrees.

Among physical properties mentioned in this specification, when themeasurement temperature affects the relevant physical property, thephysical property is a physical property measured at room temperature,unless otherwise specified.

In this specification, the term room temperature is a temperature in astate that is not particularly warmed or decreased, which may mean anyone temperature in a range of about 10° C. to 30° C., for example, atemperature of about 15° C. or more, 18° C. or more, 20° C. or more, orabout 23° C. or more, and about 27° C. or less. In addition, unlessotherwise specified, the unit of temperature referred to in thisspecification is ° C.

The phase difference, refractive index and refractive index anisotropy,and the like referred to in this specification are physical quantitieswith respect to light having a wavelength of about 550 nm, unlessotherwise specified.

Unless otherwise specified, the angle formed by any two directions,which is mentioned herein, may be an acute angle of acute angles toobtuse angles formed by the two directions, or may be a smallest anglefrom angles measured in clockwise and counterclockwise directions. Thus,unless otherwise specified, the angles mentioned herein are positive.However, in order to display the measurement direction between theangles measured in the clockwise direction or the counterclockwisedirection if necessary, the angle measured in the clockwise directionmay be represented as a positive number, and the angle measured in thecounterclockwise direction may be represented as a negative number.

In the present application, by applying a specific retardation film in aspecific arrangement, it is possible to provide a transmittance-variabledevice which does not cause problems such as a crosstalk phenomenon, arainbow phenomenon or a minoring phenomenon.

In the present application, the term transmittance-variable device maymean a device capable of switching between at least two different lightstates. Here, the different light state may mean a state where at leastthe transmittance is different.

As examples of states that the transmittance-variable device mayimplement, transparent and black mode states may be exemplified. In oneexample, the transmittance-variable device of the present applicationmay be a device capable of switching between at least the transparentand black mode states.

The transmittance of the transmittance-variable device in thetransparent mode may be at least 20% or more, 25% or more, 30% or more,35% or more, 40% or more, 45% or more, 50% or more, 55% or more, 60% ormore, 65% or more, 70% or more, 75% or more, or 80% or more or so. Also,the transmittance of the transmittance-variable device in the black modemay be 60% or less, 55% or less, 50% or less, 45% or less, 40% or less,35% or less, 30% or less, 25% or less, 20% or less, 15% or less, 10% orless, or 5% or less. Since the higher the transmittance in thetransparent mode state is, the more advantageous it is and the lower thetransmittance in the black mode state is, the more advantageous it is,the upper limit of the transmittance in the transparent mode state andthe lower limit of the transmittance in the black mode state are notparticularly limited, where in one example, the upper limit of thetransmittance in the transparent mode state may be about 100% and thelower limit of the transmittance in the black mode state may be about0%.

In one example, in the transmittance-variable device capable ofswitching between the transparent mode state and the black mode state,the difference between the transmittance in the transparent mode stateand the transmittance in the black mode state (transparent mode-blackmode) may be 15% or more, 20% or more, 25% or more, 30% or more, 35% ormore, or 40% or more, or may be 90% or less, 85% or less, 80% or less,75% or less, 70% or less, 65% or less, 60% or less, 55% or less, 50% orless, or 45% or less.

In addition, in one example, the ratio (Tmax/Tmin) of the maximumtransmittance (Tmax) in the transparent mode state to the minimumtransmittance (Tmin) in the black mode state may be in a range of about1.5 to 10. In another example, the ratio may be about 2 or more, 2.5 ormore, 3 or more, 3.5 or more, 4 or more, 4.5 or more, 5 or more, 6 ormore, or 6.5 or more, or may be about 9.5 or less, about 9 or less,about 8.5 or less, about 8 or less, about 7.5 or less, about 7 or less,about 6.5 or less, about 6 or less, about 5.5 or less, about 5 or less,about 4.5 or less, about 4 or less, about 3.5 or less, about 3 or less,about 2.5 or less, or about 2 or less.

The transmittance may be, for example, linear light transmittance. Thelinear light transmittance is a percentage of the ratio of the lighttransmitted in the same direction as the incident direction to the lightincident on the device. For example, if the device is in the form of afilm or sheet, the percentage of the light transmitted through thedevice in the direction parallel to the normal direction among the lightincident in a direction parallel to the normal direction of the film orsheet surface may be defined as the transmittance.

The transmittance or reflectance may be each transmittance orreflectance for any one wavelength in the visible light region, forexample, any one wavelength in a range of about 400 to 700 nm or about380 to 780 nm, or transmittance or reflectance for the entire visiblelight region, maximum or minimum transmittance or reflectance among thetransmittance or reflectance for the entire visible light region, or anaverage value of the transmittance or an average value of thereflectance in the visible region. In another example, the transmittancemay be transmittance for light having a wavelength of about 550 nm.

The transmittance-variable device of the present application may bedesigned to switch between at least two or more states of any one stateselected from the transparent and black mode states. If necessary, otherstates other than the above states, for example, other third states orfurther states including an intermediate transmittance state in thetransparent mode and black mode states can also be implemented.

The switching of the transmittance-variable device may be controlleddepending on whether or not an external signal, for example, a voltagesignal is applied. For example, in a state of not applying an externalsignal such as a voltage, the transmittance-variable device may maintainany one of the above-described states, and then may be switched toanother state when a voltage is applied. The state of the mode may bechanged or the third different mode state may also be implemented, bychanging the intensity, frequency and/or shape of the applied voltage.

The transmittance-variable device of the present application maycomprise at least a transmittance-variable layer for the aboveswitching. In one example, the transmittance-variable layer may be alayer that generates a polarization component. An example of such atransmittance-variable layer includes an active liquid crystal layer.

In the present application, the term active liquid crystal layer is alayer containing at least a liquid crystal compound, which may mean aliquid crystal layer capable of controlling the oriented state of theliquid crystal compound through external signal application or the like.However, the application of the active liquid crystal layer is oneexample of the present application, and if necessary, other knowntransmittance-variable layers, for example, an electrochromic materiallayer, a photochromic material layer, an electrophoretic material layeror a dispersed particle alignment layer, etc. may also be used.

The active liquid crystal layer is a layer containing a liquid crystalcompound. In this specification, all layers containing a liquid crystalcompound capable of controlling its orientation through application ofan external signal, or the like are included in the range of the termactive liquid crystal layer, and for example, as described below, aso-called guest host layer comprising a liquid crystal compound (liquidcrystal host) and a dichroic dye is also a kind of liquid crystal layerdefined in this specification. As the liquid crystal compound, any kindof liquid crystal compound can be used as long as its orientationdirection can be changed by application of an external signal. Forexample, a smectic liquid crystal compound, a nematic liquid crystalcompound or a cholesteric liquid crystal compound may be used as theliquid crystal compound. In addition, the liquid crystal compound maybe, for example, a compound having no polymerizable group orcrosslinkable group so that the orientation direction thereof may bechanged by application of an external signal.

The liquid crystal layer may comprise a liquid crystal compound whosedielectric constant anisotropy is positive or negative, or the liquidcrystal layer may exhibit the dielectric constant anisotropy mentionedabove. The absolute value of the dielectric constant anisotropy can beappropriately selected in consideration of the object of the presentapplication. The term “dielectric constant anisotropy (Δε)” may mean adifference (ε//−ε⊥) between the horizontal dielectric constant (ε//) andthe vertical dielectric constant (ε⊥). In this specification, the termhorizontal dielectric constant (ε//) means a dielectric constant valuemeasured along the direction of an electric field in a state where avoltage is applied so that the director of the liquid crystal and thedirection of the electric field by the applied voltage are substantiallyhorizontal, and the vertical dielectric constant (ε⊥) means a dielectricconstant value measured along the direction of an electric field in astate where a voltage is applied so that the director of the liquidcrystal and the direction of the electric field by the applied voltageare substantially perpendicular.

The liquid crystal layer may comprise a liquid crystal compound havingrefractive index anisotropy (Δn) in a range of about 0.03 to 0.2, or theliquid crystal layer may exhibit the aforementioned refractive indexanisotropy. The refractive index anisotropy (Δn) referred to in thepresent application is a difference (ne-no) between an extraordinaryrefractive index (ne) and an ordinary refractive index (no), which canbe confirmed using an Abbe refractometer, and the specific manner is inaccordance with the method disclosed in the following examples.

The driving mode of the liquid crystal layer may be exemplified by, forexample, a DS (dynamic scattering) mode, an ECB (electricallycontrollable birefringence) mode, an IPS (in-plane switching) mode, anFFS (fringe-field switching) mode, an OCB (optically compensated bend)mode, a VA (vertical alignment) mode, an MVA (multi-domain verticalalignment) mode, a PVA (patterned vertical alignment) mode, an HAN(hybrid aligned nematic) mode, a TN (twisted nematic) mode, an STN(super twisted nematic) mode, or the like.

The active liquid crystal layer, which is a transmittance-variablelayer, may further comprise a dichroic dye together with the liquidcrystal compound in terms of controlling light transmittance-variablecharacteristics. In this case, the active liquid crystal layer may bereferred to as a guest host liquid crystal cell described below. In thisspecification, the term “dye” may mean a material capable of intensivelyabsorbing and/or deforming light in at least a part or all of the rangeswithin a visible light region, for example, within a wavelength range of400 nm to 700 nm, and the term “dichroic dye” may mean a materialcapable of anisotropic absorption of light in at least a part or all ofthe ranges of the visible light region. Such a dye is known, forexample, as an azo dye or an anthraquinone dye, and the like, but is notlimited thereto.

In one example, the transmittance-variable layer is a liquid crystallayer comprising liquid crystal and dichroic dyes, which may be aso-called guest host liquid crystal layer (guest host liquid crystalcell). The term “GHLC layer” may mean a functional layer that dichroicdyes are arranged together depending on arrangement of liquid crystalsto exhibit anisotropic light absorption characteristics with respect toan alignment direction of the dichroic dyes and the directionperpendicular to the alignment direction, respectively. For example, thedichroic dye is a substance whose absorption rate of light varies with apolarization direction, where if the absorption rate of light polarizedin the long axis direction is large, it may be referred to as a p-typedye, and if the absorption rate of polarized light in the short axisdirection is large, it may be referred to as an n-type dye. In oneexample, when a p-type dye is used, the polarized light vibrating in thelong axis direction of the dye may be absorbed and the polarized lightvibrating in the short axis direction of the dye may be less absorbed tobe transmitted. Hereinafter, unless otherwise specified, the dichroicdye is assumed to be a p-type dye.

The ratio of the dichroic dye included in the guest host liquid crystallayer is not particularly limited, which may be set in an appropriaterange in consideration of the desired transmittance. In general, thedichroic dye may be included in the liquid crystal layer at a ratio ofabout 0.1 wt % to 4 wt % in consideration of miscibility of the dichroicdye and the liquid crystal compound.

The light modulation film layer comprising the guest host liquid crystallayer as the transmittance-variable layer may function as an activepolarizer. In this specification, the term “active polarizer” may mean afunctional element capable of controlling anisotropic light absorptiondepending on external signal application. Such an active polarizer canbe distinguished from a passive polarizer, which is described below,having constant light absorption or light reflection characteristicsregardless of the external signal application. The guest host liquidcrystal layer can control the anisotropic light absorption for thepolarized light in the direction parallel to the arrangement directionof dichroic dyes and the polarized light in the vertical direction bycontrolling the arrangement of liquid crystals and dichroic dyes. Sincethe arrangement of liquid crystals and dichroic dyes can be controlledby the application of the external signal such as a magnetic field or anelectric field, the guest host liquid crystal layer can controlanisotropic light absorption depending on the external signalapplication.

In one example, the active liquid crystal layer may be configured to becapable of switching at least between any one state of a verticalorientation mode, a horizontal orientation mode and an obliqueorientation mode and another state. The meanings of the vertical,horizontal and oblique orientation modes are in accordance with theknown content.

Thus, for example, the term horizontal orientation state may mean astate where directors of an active liquid crystal layer, which is atransmittance-variable layer, or directors of a liquid crystal compoundin the liquid crystal layer are arranged substantially parallel to thevariable layer (liquid crystal layer). In this case, the angle that thedirectors and the variable layer form on the side of the variable layer(liquid crystal layer) may be in a range of approximately 0 degrees to10 degrees or approximately 0 degrees to 5 degrees, or about 0 degrees.

Furthermore, for example, the term vertical alignment state may be astate where directors of an active liquid crystal layer, which is atransmittance-variable layer, or directors of a liquid crystal compoundin the liquid crystal layer are arranged substantially perpendicular tothe plane of the variable layer (liquid crystal layer), and for example,the angle that the directors and the variable layer (liquid crystallayer) form on the side of the variable layer (liquid crystal layer) maybe in a range of about 80 degrees to 100 degrees or 85 degrees to 95degrees, or approximately 90 degrees.

In addition, for example, the term oblique orientation state is anorientation state of an intermediate state between the verticalorientation state and the horizontal orientation state, which may mean acase where the angle that the directors of the variable layer (liquidcrystal layer) or the directors of the liquid crystal compound in theliquid crystal layer form with the variable layer (liquid crystal layer)on the side of the variable layer (liquid crystal layer) is greater than0 degrees and less than 90 degrees, or a case where it is in a range ofapproximately 10 degrees to 80 degrees.

In this specification, the director of the liquid crystal molecule orthe liquid crystal compound may mean a light axis (optical axis) or aslow axis of the active liquid crystal layer. The director of the liquidcrystal molecule may mean the long axis direction when the liquidcrystal molecule has a rod shape and may mean a normal direction axis ofthe disk plane when the liquid crystal molecule has a discotic shape.When there is a plurality of liquid crystal compounds having differentdirectors in the active liquid crystal layer, the director is a vectorsum.

In one example, the active liquid crystal layer, which is thetransmittance-variable layer, may be designed to implement at least atwist orientation mode. The term twist orientation mode may mean ahelical structure in which the directors of the liquid crystal compoundsare twisted along an imaginary helical axis in the liquid crystal layerand simultaneously oriented to form a layer. The twist orientation modemay be implemented in the above-described vertical, horizontal oroblique orientation mode, and that is, the vertical twist orientationmode is a layered state in which the individual liquid crystal compoundsare twisted along the helical axis in a vertically oriented state andthe horizontal twist orientation mode is a layered state in which theindividual liquid crystal compounds are twisted along the helical axisin a horizontally oriented state, and the oblique twist orientation modeis a layered state in which the individual liquid crystal compounds aretwisted along the helical axis in an obliquely oriented state.

In the twist orientation mode, the ratio (d/p) of the thickness (d) andthe pitch (p) of the liquid crystal layer may be 1 or less. When theratio (d/p) is greater than 1, there may be a problem that a fingerdomain or the like occurs, and thus it may be adjusted to the aboverange, if possible. The lower limit of the ratio id/p) is notparticularly limited, but may be about 0.6 or more or more than about0.6. Here, the thickness (d) of the liquid crystal layer may be the samemeaning as the cell gap of the liquid crystal cell.

The pitch (p) of the liquid crystal layer in the twist orientation modemay be measured by a measuring method using a wedge cell, andspecifically, it may be measured by a method described in Simple methodfor accurate measurement of the cholesteric pitch using a “stripe-wedgeGrandjean-Cano cell of D. Podolskyy, et al. (Liquid Crystals. Vol. 35.No. 7, July 2008, 789-791).

The liquid crystal layer may further comprise a so-called chiral agentso that the liquid crystal layer may implement a twist mode. That is,the active liquid crystal layer may comprise at least a liquid crystalcompound and a chiral agent, or may comprise at least a liquid crystalcompound, a dichroic dye and a chiral agent. The chiral agent (or chiraldopant) that can be included in the liquid crystal layer can be usedwithout particular limitation as long as it can induce a desiredrotation (twisting) without deteriorating the liquid crystallinity, forexample, the nematic regularity. The chiral agent for inducing rotationin the liquid crystal molecules needs to include at least chirality inthe molecular structure. The chiral agent may be exemplified by, forexample, a compound having one or two or more asymmetric carbons, acompound having an asymmetric point on a heteroatom, such as a chiralamine or a chiral sulfoxide, or a compound having axially asymmetric andoptically active sites such as cumulene or binaphthol. The chiral agentmay be, for example, a low molecular weight compound having a molecularweight of 1,500 or less. As the chiral agent, commercially availablechiral nematic liquid crystals, for example, chiral dopant liquidcrystal S-811 available from Merck Co., Ltd. or LC756 available fromBASF may also be used.

The application ratio of the chiral agent is selected so as to achievethe desired ratio (d/p), which is not particularly limited. In general,the content (wt %) of the chiral agent is calculated by an eluation of100/HTP (helical twisting power)×pitch (nm), and an appropriate ratiocan be selected in consideration of the desired pitch with reference tothis method.

The thicknesses of the transmittance-variable layer may each beappropriately selected in consideration of the object of the presentapplication. In one example, the thickness of the transmittance-variablelayer may be about 0.01 μm or more, 0.1 μm or more, 1 μm or more, 2 μmor more, 3 μm or more, 4 μm or more, 5 μm or more, 6 μm or more, 7 μm ormore, 8 μm or more, 9 μm or more, or 10 μm or more. By controlling thethickness in this way, a device having a large difference intransmittance according to the mode state can be realized. The thickerthe thickness, the higher the difference in transmittance and/orreflectance can be realized, and thus it is not particularly limited,but may be generally about 30 μm or less, 25 μm or less, 20 μm or less,or 15 μm or less.

The device of the present application further comprises a retardationfilm disposed on at least one side of the above-mentionedtransmittance-variable layer. FIG. 1 is a schematic diagram of a deviceaccording to one example of the present application, and shows theretardation film (100) and the variable layer (200) sequentiallyarranged.

By arranging a film having optically large anisotropy at a specificposition as the retardation film, the present application can provide adevice without a so-called rainbow phenomenon, or minoring phenomenonand crosstalk phenomenon. Incidentally, by applying an anisotropic filmin terms of mechanical properties as the retardation film, a devicehaving excellent mechanical properties can also be constituted.

In this specification, the retardation film that is anisotropic in termsof optical and mechanical properties may be referred to as an asymmetricsubstrate or an asymmetric retardation film. Here, the fact that theretardation film is optically anisotropic is a case of having in-planeretardation to be described below, and the fact that it is anisotropicin terms of mechanical properties is a case of having physicalproperties to be described below.

Hereinafter, physical properties of the retardation film mentionedherein may be physical properties of the retardation film itself, orphysical properties in a state where an electrode layer is formed on oneside of the retardation film. In this case, the electrode layer may bean electrode layer formed in a state where the retardation film isincluded in the optical device.

Measurement of physical properties of each retardation film mentionedherein is performed according to the method described in the examplesection of this specification.

In one example, the in-plane retardation of the retardation film may beabout 4,000 nm or more. The in-plane retardation is a value for lighthaving a wavelength of 550 nm.

In this specification, the in-plane retardation (Rin) may mean a valuecalculated by Equation A below.

Rin=d×(nx−ny)  [Equation A]

In Equation A, Rin is in-plane retardation, d is a thickness of theretardation film, nx is a refractive index in the in-plane slow axisdirection of the retardation film, ny is a refractive index in the fastaxis direction, which is the refractive index of the in-plane directionperpendicular to the slow axis direction.

The in-plane retardation of the retardation film may each be 4,500 nm ormore, 5,000 nm or more, 6,000 nm or more, 7,000 nm or more, 8,000 nm ormore, 9,000 nm or more, 10,000 nm or more, 11,000 nm or more, 12,000 nmor more, 13,000 nm or more, 14,000 nm or more, or 15,000 nm or more orso. The in-plane retardation of the retardation film may each be about50,000 nm or less, about 40.000 nm or less, about 30,000 nm or less,20,000 nm or less, 18,000 nm or less, 16,000 nm or less, 15,000 nm orless, or 12,000 nm or less or so.

As a film having large retardation as above, a film known as a so-calledhigh-stretched PET (poly(ethylene terephthalate) film or SRF (superretardation film), and the like is typically known. Therefore, in thepresent application, the retardation film may be, for example, apolyester film.

The film having extremely high retardation as above is known in the art,and such a film exhibits high asymmetry even in mechanical properties byhigh stretching or the like during preparation procedures as well asoptically large anisotropy. A representative example of the retardationfilm in a state known in the art is a polyester film such as a PET(poly(ethylene terephthalate)) film, and for example, there are films ofthe trade name SRF (super retardation film) series supplied by ToyoboCo., Ltd.

In one example, in the retardation films, a ratio (E1/E2) of anelongation (E1) in any first direction in the plane to an elongation(E2) in a second direction perpendicular to the first direction may be 3or more. In another example, the ratio (E1/E2) may be about 3.5 or more,4 or more, 4.5 or more, 5 or more, 5.5 or more, 6 or more, or 6.5 ormore. In another example, the ratio (E1/E2) may be about 20 or less, 18or less, 16 or less, 14 or less, 12 or less, 10 or less, 8 or less, or7.5 or less.

In this specification, the terms “first direction,” “second direction”and “third direction” of the retardation film are each any in-planedirection of the film. For example, when the retardation film is astretched retardation film, the in-plane direction may be an in-planedirection formed by MD (machine direction) and TD (transverse direction)directions of the retardation film. In one example, the first directiondescribed herein may be any one of the slow axis direction and the fastaxis direction of the retardation film, and the second direction may bethe other of the slow axis direction and the fast axis direction. Inanother example, when the retardation film is a stretched retardationfilm, the first direction may be any one of MD (machine direction) andTD (transverse direction) directions, and the second direction may bethe other of MD (machine direction) and TD (transverse direction)directions.

In one example, the first direction of the retardation film mentionedherein may be the TD direction or the slow axis direction.

The retardation film may have the elongation in the first direction (forexample, the above-described slow axis direction or TD direction) of 15%or more, or 20% or more. In another example, the elongation may be about25% or more, 30% or more, 35% or more, or 40% or more, or may be about60% or less, 55% or less, 50% or less, or 45% or less.

In one example, in the retardation film, an elongation (E3) in a thirddirection, which forms an angle within a range of 40 degrees to 50degrees or about 45 degrees with each the first and second directions,respectively, is larger than the elongation (E1) in the first direction,where the ratio (E3/E2) of the elongation (E3) in the third direction tothe elongation (E2) in the second direction may be 5 or more.

In another example, the ratio (E3/E2) may be 5.5 or more, 6 or more, 6.5or more, 7 or more, 7.5 or more, 8 or more, or 8.5 or more, and may beabout 20 or less, 18 or less, 16 or less, 14 or less, 12 or less, or 10or less.

The retardation film may have the elongation in the third direction of30% or more. In another example, the elongation may be about 35% ormore, 40% or more, 45% or more, 50% or more, or 55% or more, or may beabout 80% or less, 75% or less, 70% or less, or 65% or less.

In the retardation film, a ratio (CTE2/CTE1) of a coefficient of thermalexpansion (CTE2) in the second direction to a coefficient of thermalexpansion (CTE1) in the first direction may be 1.5 or more. Thecoefficients of thermal expansion (CTE1, CTE2) are each a valueconfirmed within a temperature range of 40° C. to 80° C. In anotherexample, the ratio (CTE2/CTE1) may be about 2 or more, about 2.5 ormore, 3 or more, or 3.5 or more, or may be 10 or less, 9 or less, 8 orless, 7 or less, 6 or less, 5 or less, or 4 or less.

The coefficient of thermal expansion (CTE2) in the second direction maybe in a range of 5 to 150 ppm/° C. The coefficient of thermal expansionmay be about 10 ppm/° C. or more, 15 ppm/° C. or more, 20 ppm/° C. ormore, 25 ppm/° C. or more, 30 ppm/° C. or more, 35 ppm/° C. or more, 40ppm/° C. or more, 45 ppm/° C. or more, 50 ppm/° C. or more, 55 ppm/° C.or more, 60 ppm/° C. or more, 65 ppm/° C. or more, 70 ppm/° C. or more,75 ppm/° C. or more, or 80 ppm/° C. or more, or may be 140 ppm/° C. orless, 130 ppm/° C. or less, 120 ppm/° C. or less, 100 ppm/° C. or less,95 ppm/° C. or less, 90 ppm/° C. or less, 85 ppm/° C. or less, 80 ppm/°C. or less, 40 ppm/° C. or less, 30 ppm/° C. or less, or 25 ppm/° C. orless.

In the retardation film, a ratio (YM1/YM2) of an elastic modulus (YM1)in the first direction to an elastic modulus (YM2) in the seconddirection may be 1.5 or more. In another example, the ratio (YM1/YM2)may be about 2 or more, or may be 10 or less, 9 or less, 8 or less, 7 orless, 6 or less, 5 or less, 4 or less, 3 or less or 2.5 or less.

The elastic modulus (YM1) in the first direction may be in a range ofabout 2 to 10 GPa. In another example, the elastic modulus (YM1) may beabout 2.5 GPa or more, 3 GPa or more, 3.5 GPa or more, 4 GPa or more,4.5 GPa or more, 5 GPa or more, or 5.5 GPa or more, or may also be about9.5 GPa or less, 9 GPa or less, 8.5 GPa or less, 8 GPa or less, 7.5 GPaor less, 7 GPa or less, 6.5 GPa or less, or 6 GPa or less.

The elastic modulus may mean a so-called Young's modulus.

In the retardation film, a ratio (MS1/MS2) of a maximum stress (MS1) inthe first direction to a maximum stress (MS2) in the second directionmay be 1.5 or more. In another example, the ratio (MS1/MS2) may be about2 or more, or may be 10 or less, 9 or less, 8 or less, 7 or less, 6 orless, 5 or less, 4 or less, 3 or less, or 2.5 or less.

The maximum stress (MS1) in the first direction (for example, theabove-described slow axis direction or TD direction) may be in a rangeof about 80 to 300 MPa. In another example, the maximum stress (MS1) maybe about 90 MPa or more, about 100 MPa or more, about 110 MPa or more,about 120 MPa or more, about 130 MPa or more, about 140 MPa or more,about 150 MPa or more, about 155 MPa or more, 160 MPa or more, 165 MPaor more, 170 MPa or more, 175 MPa or more, or 180 MPa or more, or mayalso be about 300 MPa or less, about 290 MPa or less, about 280 MPa orless, about 270 MPa or less, about 260 MPa or less, about 250 MPa orless, about 245 MPa or less, 240 MPa or less, 235 MPa or less, 230 MPaor less, 225 MPa or less, 220 MPa or less, 215 MPa or less, 210 MPa orless, 205 MPa or less, 200 MPa or less, 195 MPa or less, or 190 MPa orless.

As described above, a representative example of the polymer film havinglarge optical and mechanical asymmetry as above is a stretched PET(polyethyleneterephthalate) film known as a so-called high stretchedpolyester film or the like, and such a film is easily available in theindustry.

Usually, the stretched PET film is a uniaxially stretched film of one ormore layers produced by forming a PET-based resin into a film withmelting/extruding, and stretching it or a biaxially stretched film ofone or more layers produced by longitudinally and transverselystretching it after film formation.

The PET-based resin generally means a resin in which 80 mol % or more ofthe repeating units are ethylene terephthalate, which may also containother dicarboxylic acid components and diol components. Otherdicarboxylic acid components are not particularly limited, but mayinclude, for example, isophthalic acid, p-beta-oxyethoxybenzoic acid,4,4′-dicarboxydiphenyl, 4,4′-dicarboxybenzophenone,bis(4-carboxyphenyl)ethane, adipic acid, sebacic acid and/or1,4-dicarboxycyclohexane, and the like.

Other diol components are not particularly limited, but may includepropylene glycol, butanediol, neopentyl glycol, diethylene glycol,cyclohexanediol, ethylene oxide adducts of bisphenol A, polyethyleneglycol, polypropylene glycol and/or polytetramethylene glycol, and thelike.

The dicarboxylic acid component or the diol component may be used incombination of two or more as necessary. Furthermore, an oxycarboxylicacid such as p-oxybenzoic acid may also be used in combination. Inaddition, as other copolymerization components, a dicarboxylic acidcomponent containing a small amount of amide bonds, urethane bonds,ether bonds and carbonate bonds, and the like, or a diol component mayalso be used.

As a production method of the PET-based resin, a method of directlypolycondensing terephthalic acid, ethylene glycol and/or, as necessary,other dicarboxylic acids or other diols, a method of transesterifyingdialkyl ester of terephthalic acid and ethylene glycol and/or, asnecessary, dialkyl esters of other dicarboxylic acids or other diols andthen polycondensing them, and a method of polycondensing terephtalicacid and/or, as necessary, ethylene glycol esters of other dicarboxylicacids and/or, as necessary, other diolesters, and the like are adopted.

For each polymerization reaction, a polymerization catalyst containingan antimony-based, titanium-based, germanium-based or aluminum-basedcompound, or a polymerization catalyst containing the composite compoundcan be used.

The polymerization reaction conditions can be appropriately selecteddepending on monomers, catalysts, reaction apparatuses and intendedresin physical properties, and are not particularly limited, but forexample, the reaction temperature is usually about 150′ C. to about 300°C., about 200° C. to about 300° C. or about 260° C. to about 300° C.Furthermore, the reaction pressure is usually atmospheric pressure toabout 2.7 Pa, where the pressure may be reduced in the latter half ofthe reaction.

The polymerization reaction proceeds by volatilizing leaving reactantssuch as a diol, an alkyl compound or water.

The polymerization apparatus may also be one which is completed by onereaction tank or connects a plurality of reaction tanks. In this case,the reactants are polymerized while being transferred between thereaction tanks, depending on the degree of polymerization. In addition,a method, in which a horizontal reaction apparatus is provided in thelatter half of the polymerization and the reactants are volatilizedwhile heating/kneading, may also be adopted.

After completion of the polymerization, the resin is discharged from thereaction tank or the horizontal reaction apparatus in a molten state,and then, obtained in the form of flakes cooled and pulverized in acooling drum or a cooling belt, or in the form of pellets tailored afterbeing introduced into an extruder and extruded in a string shape.Furthermore, solid-phase polymerization may be performed as needed,thereby improving the molecular weight or decreasing the low molecularweight component. As the low molecular weight component that may becontained in the PET-based resin, a cyclic trimer component may beexemplified, but the content of such a cyclic trimer component in theresin is usually controlled to 5,000 ppm or less, or 3.000 ppm or less.

The molecular weight of the PET-based resin is usually in a range of0.45 to 1.0 dL/g, 0.50 to 1.0 dL/g or 0.52 to 0.80 dL/g, when the resinhas been dissolved in a mixed solvent of phenol/tetrachloroethane=50/50(weight ratio) and it has been represented as a limiting viscositymeasured at 30° C.

In addition, the PET-based resin may contain additives as required. Theadditive may include a lubricant, an anti-blocking agent, a heatstabilizer, an antioxidant, an antistatic agent, a light stabilizer andan impact resistance improver, and the like. The addition amount thereofis preferably within a range that does not adversely affect the opticalproperties.

The PET-based resin is used in the form of pellets assembled by anordinary extruder, for formulation of such additives and film molding tobe described below. The size and shape of the pellets are notparticularly limited, but they are generally a cylindrical, spherical orflat spherical shape having both height and diameter of 5 mm or less.The PET-based resin thus obtained can be molded into a film form andsubjected to a stretching treatment to obtain a transparent andhomogeneous PET film having high mechanical strength. The productionmethod thereof is not particularly limited, and for example, thefollowing method is adopted.

Pellets made of the dried PET resin are supplied to a melt extrusionapparatus, heated to a melting point or higher and melted. Next, themelted resin is extruded from the die and quenched and solidified on arotary cooling drum to a temperature below the glass transitiontemperature to obtain an un-stretched film in a substantially amorphousstate. This melting temperature is determined according to the meltingpoint of the PET-based resin to be used or the extruder, which is notparticularly limited, but is usually 250° C. to 350° C. In order toimprove planarity of the film, it is also preferred to enhance adhesionbetween the film and the rotary cooling drum, and an adhesion method byelectrostatic application or an adhesion method by liquid coating ispreferably adopted. The adhesion method by electrostatic application isusually a method in which linear electrodes are provided on the uppersurface side of a film in a direction perpendicular to the flow of thefilm and a direct current voltage of about 5 to 10 kV is applied to theelectrodes to provide static charges to the film, thereby improving theadhesion between the rotary cooling drum and the film. In addition, theadhesion method by liquid coating is a method for improving the adhesionbetween the rotary cooling drum and the film by uniformly coating aliquid to all or a part (for example, only the portion in contact withboth film ends) of the surface of the rotary cooling drum. Both of themmay also be used in combination if necessary. The PET-based resin to beused may be mixed with two or more resins, or resins having differentstructures or compositions, if necessary. For example, it may includeusing a mixture of pellets blended with a particulate filling materialas an anti-blocking agent, an ultraviolet absorbing agent or anantistatic agent, and the like, and non-blended pellets, and the like.

Furthermore, the laminating number of films to be extruded may also betwo or more layers, if necessary. For example, it may include thatpellets blended with a particulate filling material as an anti-blockingagent and non-blended pellets are prepared and supplied from the otherextruder to the same die to extrude a film composed of two kinds andthree layers, “blended with filling material/non-blended/blended withfilling material,” and the like.

The un-stretched film is usually stretched longitudinally at atemperature not lower than the glass transition temperature in theextrusion direction first. The stretching temperature is usually 70 to150° C., 80 to 130° C., or 90 to 120° C. In addition, the stretchingratio is usually 1.1 to 6 times or 2 to 5.5 times. The stretching may beterminated once or divided into more than once as necessary.

The longitudinally stretched film thus obtained may be subjected to aheat treatment thereafter. Then, a relaxation treatment may be performedif necessary. The heat treatment temperature is usually 150 to 250° C.,180 to 245° C. or 200 to 230° C. Also, the heat treatment time isusually 1 to 600 seconds or 1 to 300 seconds or 1 to 60 seconds.

The temperature of the relaxation treatment is usually 90 to 200° C. or120 to 180° C. Also, the amount of relaxation is usually 0.1 to 20% or 2to 5%. The relaxation treatment temperature and the relaxation amountcan be set so that a heat shrinkage rate of the PET film afterrelaxation treatment at 150° C. is 2% or less.

In the case of obtaining uniaxially stretched and biaxially stretchedfilms, transverse stretching is usually performed by a tenter after thelongitudinal stretching treatment or after the heat treatment orrelaxation treatment, if necessary. The stretching temperature isusually 70 to 150° C., 80 to 130° C., or 90 to 120° C. In addition, thestretching ratio is usually 1.1 to 6 times or 2 to 5.5 times.Thereafter, the heat treatment and, if necessary, the relaxationtreatment can be performed. The heat treatment temperature is usually150 to 250° C. or 180 to 245° C. or 200 to 230° C. The heat treatmenttime is usually 1 to 600 seconds, 1 to 300 seconds, or 1 to 60 seconds.

The temperature of the relaxation treatment is usually 100 to 230° C.,110 to 210° C. or 120 to 180° C. Also, the relaxation amount is usually0.1 to 20%, 1 to 10%, or 2 to 5%. The relaxation treatment temperatureand the relaxation amount can be set so that the heat shrinkage rate ofthe PET film after the relaxation treatment at 150° C. is 2% or less.

In uniaxial stretching and biaxial stretching treatments, after thetransverse stretching, in order to alleviate deformation of theorientation main axis as represented by bowing, the heat treatment canbe performed again or the stretching treatment can be performed afterthe transverse stretching. The maximum value of deformation in theorientation main axis by bowing with respect to the stretching directionis usually within 45 degrees, within 30 degrees, or within 15 degrees.Here, the stretching direction also refers to a stretching largedirection in longitudinal stretching or transverse stretching.

In the biaxial stretching of the PET film, the transverse stretchingratio is usually slightly larger than the longitudinal stretching ratio,where the stretching direction refers to a direction perpendicular tothe long direction of the film. Also, the uniaxial stretching is usuallystretched in the transverse direction as described above, where thestretching direction equally refers to a direction perpendicular to thelong direction.

Also, the orientation main axis refers to a molecular orientationdirection at any point on the stretched PET film. Furthermore, thedeformation of the orientation main axis with respect to the stretchingdirection refers to an angle difference between the orientation mainaxis and the stretching direction. In addition, the maximum valuethereof refers to a maximum value of the values on the verticaldirection with respect to the long direction.

The direction of identifying the orientation main axis is known, and forexample, it can be measured using a retardation film/optical materialinspection apparatus RETS (manufactured by Otsuka Densi KK) or amolecular orientation system MOA (manufactured by Oji ScientificInstruments).

The functional layer other than the antiglare layer or the like can belaminated on one side or both sides of the stretched PET film, unless itinterferes with the effect of the present application. The functionallayer to be laminated may include, for example, a conductive layer, ahard coating layer, a smoothing layer, an easily slipping layer, ananti-blocking layer and an easy adhesion layer, and the like.

The above-described production method is one exemplary method forobtaining the retardation film of the present application, where as longas the retardation film applicable in the present application has theabove-described physical properties, any kind of commercially availableproduct can also be used.

In the device of the present application, the retardation film isincluded in the device so that the slow axis of the film has a specificpositional relationship.

In one example, the device may comprise a liquid crystal alignment film,which is described below, between the retardation film and thetransmittance-variable layer, where the angle formed between the slowaxis of the retardation film and the alignment direction of the liquidcrystal alignment film may be in a range of 0 degrees to 70 degrees.FIG. 2 is a schematic diagram of a case where the retardation film(100), the liquid crystal alignment film (300), and thetransmittance-variable layer (200) are arrange sequentially in theillustration. The angle is a smallest angle among the angles formed bythe alignment direction and the slow axis, and in one example, it may bein a range of 0 degrees to 360 degrees or so. In another example, theangle may be more than 0 degrees, 2 degrees or more, 4 degrees or more,6 degrees or more, 8 degrees or more, 10 degrees or more, 12 degrees ormore, 14 degrees or more, 16 degrees or more, 18 degrees or more, 20degrees or more, 22 degrees or more, 24 degrees or more, 26 degrees ormore, 28 degrees or more, 30 degrees or more, 32 degrees or more, 34degrees or more, 36 degrees or more, 38 degrees or more, 40 degrees ormore, 42 degrees or more, 44 degrees or more, 46 degrees or more, 48degrees or more, or 50 degrees or more, or may also be less than 360degrees, 350 degrees or less, 340 degrees or less, 330 degrees or less,320 degrees or less, 310 degrees or less, 300 degrees or less, 290degrees or less, 280 degrees or less, 270 degrees or less, 260 degreesor less, 250 degrees or less, 240 degrees or less, 230 degrees or less,220 degrees or less, 210 degrees or less, 200 degrees or less, 190degrees or less, 180 degrees or less, 170 degrees or less, 160 degreesor less, 150 degrees or less, 140 degrees or less, 130 degrees or less,120 degrees or less, 110 degrees or less, 100 degrees or less, 90degrees or less, 80 degrees or less, 70 degrees or less, or 60 degreesor less or so. The liquid crystal alignment film may be used todetermine the initial orientation of the liquid crystals in the liquidcrystal layer when the transmittance-variable layer is an active liquidcrystal layer. The kind of liquid crystal alignment film applied at thistime is not particularly limited, which may be, for example, a knownrubbing alignment film or photo-alignment film. As described below, thealignment film may exist on both sides of the active liquid crystallayer, and in this case, the alignment film having the alignmentdirection of the angle with the slow axis of the retardation film is analignment direction of the alignment film located close to theretardation film. The alignment direction may be the rubbing directionin the case of the rubbing alignment film and the direction of polarizedlight to be irradiated in the case of the photo-alignment film, wheresuch an alignment direction may be confirmed by a detection method usinga linear polarizer. For example, in the case of being the liquid crystallayer (transmittance-variable layer) in a twist orientation mode such asan STN (super twisted nematic) mode, upon disposing a linear polarizeron one side and measuring the transmittance while changing theabsorption axis of the polarizer, the transmittance tends to be low whenthe alignment direction of the liquid crystal alignment film coincideswith the absorption axis or the transmission axis, where the alignmentdirection can be confirmed through simulation reflecting refractiveindex anisotropy of the applied liquid crystal compound and the like.The method of confirming an alignment direction according to the mode ofthe liquid crystal layer (transmittance-variable layer) is known, and inthe present application, the angle formed by the alignment direction ofthe liquid crystal alignment film and the slow axis can be confirmed bysuch a known method.

In another example, in the case where the transmittance-variable layeris an active liquid crystal layer capable of implementing theabove-described twist orientation mode, upon measuring the angle betweenthe slow axis of the retardation film and the alignment direction of theliquid crystal alignment film along the twisting direction of the twistorientation mode in the alignment direction of the liquid crystalalignment film, the retardation film may be disposed so that it is inthe range of 0 degrees to 360 degrees. In another example, the angle maybe more than 0 degrees, 2 degrees or more, 4 degrees or more, 6 degreesor more, 8 degrees or more, 10 degrees or more, 12 degrees or more, 14degrees or more, 16 degrees or more, 18 degrees or more, 20 degrees ormore, 22 degrees or more, 24 degrees or more, 26 degrees or more, 28degrees or more, 30 degrees or more, 32 degrees or more, 34 degrees ormore, 36 degrees or more, 38 degrees or more, 40 degrees or more, 42degrees or more, 44 degrees or more, 46 degrees or more, 48 degrees ormore, or 50 degrees or more, or may also be less than 360 degrees, 350degrees or less, 340 degrees or less, 330 degrees or less, 320 degreesor less, 310 degrees or less, 300 degrees or less, 290 degrees or less,280 degrees or less, 270 degrees or less, 260 degrees or less, 250degrees or less, 240 degrees or less, 230 degrees or less, 220 degreesor less, 210 degrees or less, 200 degrees or less, 190 degrees or less,180 degrees or less, 170 degrees or less, 160 degrees or less, 150degrees or less, 140 degrees or less, 130 degrees or less, 120 degreesor less, 110 degrees or less, 100 degrees or less, 90 degrees or less,80 degrees or less, 70 degrees or less, or 60 degrees or less or so.Here, the meaning of the alignment direction of the liquid crystalalignment film and a method of determining the same are as describedabove, and the twisting direction in the liquid crystal layer of thetwist mode may be measured through rotation direction analyses of thepolarized light source emitted from the transmittance-variable layerusing a measuring instrument such as Exoscan. In such a case, thetwisting direction may be clockwise or counterclockwise.

In another example, the arrangement of the retardation film may also becontrolled in consideration of the twisting angle of the twistorientation mode, the refractive index anisotropy of thetransmittance-variable layer (active liquid crystal layer) and/or thethickness of the variable layer (active liquid crystal layer).

For example, when the twist angle in the twist orientation mode of thevariable layer is in a range of 50 degrees to 180 degrees or in a rangeof 80 degrees to 180 degrees, the smallest angle among the anglesbetween the slow axis of the retardation film and the alignmentdirection of the liquid crystal alignment film, or the angle between theslow axis and the alignment direction measured along the twistingdirection of the twist orientation mode in the alignment direction ofthe liquid crystal alignment film may satisfy Equation 1 below.

0.05×Δnd×T/μm+10≤A≤0.16×Δnd×T/μm+60  [Equation 1]

In Equation 1, A is the smallest angle among the angles formed by thealignment direction of the liquid crystal alignment film or the anglebetween the slow axis and the alignment direction measured along thetwisting direction of the twist orientation mode in the alignmentdirection of the liquid crystal alignment film (unit: degree), Δn is therefractive index anisotropy of the variable layer (active liquid crystallayer) for light having a wavelength of 550 nm, d is the thickness(unit: μm) of the liquid crystal layer, and T is the twist angle (unit:degree) of the twist orientation mode.

The method of confirming the twisting direction of the twist orientationmode for confirming whether or not the equation is satisfied is asdescribed above, and the twist angle can be calculated back or estimatedby way of polarized light analyses reflecting the refractive indexanisotropy of the liquid crystal compound and the cell gap through aknown measurement method such as Exoscan. or after checking the pitch ofthe liquid crystal layer using Wedge Cell, it can be estimated throughthe pitch value relative to the cell gap.

When Equation 1 above is satisfied, the product (Δnd) of the refractiveindex anisotropy (Δn) of the liquid crystal layer for light having awavelength of 550 nm and the thickness (d) of the liquid crystal layermay be 0.7 μm or less. In another example, the product (Δnd) of therefractive index anisotropy (Δn) and the thickness (d) of the liquidcrystal layer may be about 0.2 μm or more, 0.25 μm or more, 0.3 μm ormore, 0.35 μm or more, 0.4 μm or more, or 0.45 μm or more.

Also, in another example, the angle A in Equation 1 above may be(0.05×Δnd×T/μm+11) or more, (0.05×Δnd×T/μm+12) or more,(0.05×Δnd×T/μm+13) or more, (0.05×Δnd×T/μm+14) or more,(0.05×Δnd×T/μm+15) or more, (0.05×Δnd×T/μm+16) or more,(0.05×Δnd×T/μm+17) or more, (0.05×Δnd×T/μm+18) or more,(0.05×Δnd×T/μm+19) or more. (0.05×Δnd×T/μm+20)) or more, or(0.05×Δnd×T/μm+21) or more.

The angle A in Equation 1 above may also be (0.16×Δnd×T/μm+55) or less,(0.16×Δnd×T/μm+50) or less, (0.16×Δnd×T/μm+45) or less,(0.16×Δnd×T/μm+40) or less, (0.16×Δnd×T/μm+35) or less,(0.16×Δnd×T/μm+30) or less, (0.16×Δnd×T/μm+25) or less,(0.16×Δnd×T/μm+20) or less, (0.16×Δnd×T/μm+15) or less,(0.16×Δnd×T/μm+10) or less, (0.16×Δnd×T/μm+5) or less, or(0.16×Δnd×T/μm+1) or less or so.

In another example, when the twist angle in the twist orientation modeof the variable layer is in a range of 50 degrees to 180 degrees or 80degrees to 180 degrees, the smallest angle among the angles formed bythe slow axis of the retardation film and the alignment direction of theliquid crystal alignment film or the angle between the slow axis and thealignment direction measured along the twisting direction of the twistorientation mode in the alignment direction of the liquid crystalalignment film may also satisfy Equation 2 below.

0.16×Δnd×T/μm−10≤A≤0.16×Δnd×T/μm+20  [Equation 2]

In Equation 2, A is the smallest angle among the angles formed by thealignment direction of the liquid crystal alignment film or the anglebetween the slow axis and the alignment direction measured along thetwisting direction of the twist orientation mode in the alignmentdirection of the liquid crystal alignment film (unit: degree), Δn is therefractive index anisotropy of the variable layer (active liquid crystallayer) for light having a wavelength of 550 nm, d is the thickness(unit: μm) of the liquid crystal layer, and T is the twist angle (unit:degree) of the twist orientation mode.

The method of confirming the twisting direction and the twist angle ofthe twist orientation mode for confirming whether or not the equation issatisfied is as described above.

When Equation 2 is satisfied, the product (Δnd) of the refractive indexanisotropy (Δn) of the liquid crystal layer for light having awavelength of 550 nm and the thickness (d) of the liquid crystal layermay be more than 0.7 μm. In another example, the product (Δnd) of therefractive index anisotropy (Δn) and the thickness (d) of the liquidcrystal layer may be about 2 m or less, 1.5 μm or less, or about 1 μm orless.

Also, in another example, the angle A in Equation 2 above may be(0.16×Δnd×T/μm−8) or more. (0.16×Δnd×T/μm−6) or more. (0.16×Δnd×T/μm−4)or more, (0.16×Δnd×T/μm−2) or more, (0.16×Δnd×T/μm) or more,(0.16×Δnd×T/μm+2) or more, (0.16×Δnd×T/μm+4) or more, or(0.16×Δnd×T/μm+6) or more.

In addition, the angle A in Equation 2 above may also be(0.16×Δnd×T/μm+18) or less, (0.16×Δnd×T/μm+16) or less,(0.16×Δnd×T/μm+14)) or less, (0.16×Δnd×T/μm+12) or less,(0.16×Δnd×T/μm+10) or less, (0.16×Δnd×T/μm+8) or less, (0.16×Δnd×T/μm+6)or less, (0.16×Δnd×T/μm+4) or less, (0.16×Δnd×T/μm+2) or less, or(0.16×Δnd×T/μm) or less or so.

In another example, when the twist angle in the twist orientation modeof the variable layer is 180 degrees or more or more than 180 degrees,the smallest angle among the angles formed by the slow axis of theretardation film and the alignment direction of the liquid crystalalignment film or the angle between the slow axis and the alignmentdirection measured along the twisting direction of the twist orientationmode in the alignment direction of the liquid crystal alignment film maysatisfy Equation 3 below, or the largest angle among the angles formedby the slow axis of the retardation film and the alignment direction ofthe liquid crystal alignment film or the angle between the slow axis andthe alignment direction measured along the reverse direction of thetwisting direction of the twist orientation mode in the alignmentdirection of the liquid crystal alignment film may satisfy Equation 4below.

A=(42±5)+(17±5)×sin(2Δn×d×f)  [Equation 3]

Δ=(132±5)+(17±5)×sin(2Δn×d×f)  [Equation 4]

In Equations 3 and 4. An is the refractive index anisotropy of theliquid crystal layer for light having a wavelength of 550 nm, d is thethickness (unit: m) of the liquid crystal layer, and f is the twistangle of the twist orientation mode (unit: degree).

Furthermore. A in Equation 3 is the smallest angle among the anglesformed by the slow axis of the retardation film and the alignmentdirection of the liquid crystal alignment film or the angle between theslow axis and the alignment direction measured along the twistingdirection of the twist orientation mode in the alignment direction ofthe liquid crystal alignment film (unit: degree), and A in Equation 4 isthe largest angle among the angles formed by the slow axis of theretardation film and the alignment direction of the liquid crystalalignment film or the angle between the slow axis and the alignmentdirection measured along the reverse direction of the twisting directionof the twist orientation mode in the alignment direction of the liquidcrystal alignment film (unit: degree).

The method of confirming the twisting direction and the twist angle ofthe twist orientation mode for confirming whether or not the equation issatisfied is as described above.

When Equation 3 or 4 is satisfied, the twist angle may be about 6(0)degrees or less, 550 degrees or less, 500 degrees or less, 450 degreesor less, 400 degrees or less, 350 degrees or less, 300 degrees or less,250 degrees or less, or 200 degrees or less or so.

When Equation 3 or 4 is satisfied, the product (Δnd) of the refractiveindex anisotropy (Δn) of the liquid crystal layer for light having awavelength of 550 nm and the thickness (d) of the liquid crystal layermay be in a range of 0.2 μm to 2 μm. In another example, the product(Δnd) of the refractive index anisotropy (Δn) and the thickness (d) ofthe liquid crystal layer may be about 0.25 μm or more, 0.3 μm or more,0.35 μm or more, 0.4 μm or more, or 0.45 μm or more, or may be about 1.5μm or less, or about 1 μm or less or so.

Also, in another example, the angle A in Equation 3 may be(42±4)+(17±4)×sin(2Δnd×f), (42±3)+(17±2)×sin(2Δn×d×f),(42±2)+(17±2)×sin(2Δn×d×f), (42±1)+(17±1)×sin(2Δn×d×f) or(42+17×sin(2Δn×d×f)), and in another example, the angle A in Equation 4may be (132±4)+(17±4)×sin(2Δn×d×f), (132±3)+(17±3)×sin(2Δn×d×f),(132±2)+(17±2)×sin(2Δn×d×f), (132±1)+(17±1)×sin(2Δn×d×f) or132+17×sin(2Δn×d×f).

By arranging the retardation film having high optical anisotropydescribed above in the above positional relationship, it is possible toprovide a device without rainbow phenomenon, mirroring phenomenon andcrosstalk phenomenon while having excellent transmittance-variablecharacteristics.

The refractive index anisotropy (Δn) applied to the above-mentionedequations is measured using an Abbe refractometer according to themethod disclosed in Examples, as described above, and the method ofmeasuring the thickness (d) of the liquid crystal layer, that is, thecell gap is also according to the method disclosed in Examples.

As long as the transmittance-variable device of the present applicationcomprises the transmittance-variable layer and the retardation film, andthe arrangement therebetween is controlled as mentioned above, it may beconfigured in various ways.

For example, basically, the transmittance-variable layer, in particular,the active liquid crystal layer is positioned between two substratesdisposed opposite to each other, where any one of the two substrates mayalso be formed of the above-described retardation film in order toimplement the device of the present application (first method).

Alternatively, the device of the present application may also beimplemented by a method of attaching the retardation film to the outsideof an element comprising a transmittance-variable layer positionedbetween two substrates disposed opposite to each other (second method).

FIG. 3 is an example of implementing a device according to the firstmethod, and such a device may comprise the retardation film (100), theelectrode layer (400), the alignment film (300), the active liquidcrystal layer (200), and the alignment film (500), the electrode layer(400) and the substrate (600) which are disposed sequentially.

In addition. FIG. 4 is an example of implementing a device according tothe second method, and such a device may comprise the retardation film(100), the substrate (600), the electrode layer (400), the alignmentfilm (300), the active liquid crystal layer (200), the alignment film(500), the electrode layer (400) and the substrate (600) which aredisposed sequentially.

That is, when the device is implemented in the first method, theretardation film is applied as the substrate, where the above-describedliquid crystal alignment film may be formed on the surface of theretardation film, and when the device is implemented in the secondmethod, the device further comprises the substrate that the liquidcrystal alignment film is formed on the surface thereof, where theretardation film may be attached to the surface on which the liquidcrystal alignment film of the substrate is not formed.

The electrode layer (400), which may be included in the device, is acomponent for applying power to the active liquid crystal layer (200) asan external signal, and as such an electrode layer, a known transparentelectrode layer may be applied. For example, a so-called conductivepolymer layer, a conductive metal layer, a conductive nanowire layer, ora metal oxide layer such as ITO (indium tin oxide) may be used as theelectrode layer. Besides, various materials and forming methods capableof forming a transparent electrode layer are known, which can be appliedwithout limitation.

As the liquid crystal alignment film included in the device, a knownrubbing alignment film or a photo-alignment film, and the like may beapplied, as described above, and the type of alignment film that may beapplied according to a desired mode is known.

The kind of substrate (reference numeral 600 in FIGS. 3 and 4 ) that canbe applied in the device is not particularly limited. As the substrate,the aforementioned retardation film itself may also be applied as thepolymer film substrate, or other known substrates may also be applied.

For example, as the substrate, a glass film, a crystalline or amorphoussilicon film, an inorganic film such as quartz or ITO (indium tin oxide)film or a plastic film, and the like can be used. As the plasticsubstrate, a substrate comprising TAC (triacetyl cellulose); a COP(cyclo olefin copolymer) such as a norbornene derivative; PMMA(poly(methyl methacrylate), PC (polycarbonate); PE (polyethylene); PP(polypropylene); PVA (polyvinyl alcohol); DAC (diacetyl cellulose), Pac(polyacrylate); PES (poly ether sulfone); PEEK (polyetheretherketone);PPS (polyphenylsulfone), PEI (polyetherimide); PEN(polyethylenenaphthalate); PET (polyethyleneterephtalate); PI(polyimide); PSF (polysulfone); PAR (polyarylate) or an amorphousfluorine resin, and the like can be used, without being limited thereto.

The device basically comprises the retardation film, the liquid crystalalignment film and the transmittance-variable layer as described above,which may also further comprise various known configurations as long astheir positional relationship and the like are set as mentioned above.

For example, although not shown in the drawings, it may comprise a knowncomponent, for example, a spacer or a sealant, and the like formaintaining the distance between substrates in addition to thesubstrate, the transmittance-variable layer, and the like.

Also, it may further comprise, as other components, known componentssuch as a pressure-sensitive adhesive or an adhesive applied as a usefor attaching the retardation film to the substrate or other uses, ahard coating layer, an antireflection layer and a layer including a dyehaving a NIR (near-infrared) cut function. In addition, if necessary,the device may or may not comprise a passive polarizing layer, forexample, a passive polarizing layer such as a PVA (poly(vinyl alcohol))series polarizing layer.

Such transmittance-variable devices can be applied to variousapplications. The applications to which the transmittance-variabledevice can be applied can be exemplified by openings in closed spacesincluding buildings, containers or vehicles, and the like, such aswindows or sunroofs, eyewear, windows and the like, and light blockingpanels of OLEDs (organic light emitting devices), and the like. Here, inthe range of eyewear, all eyewear formed so that an observer can observethe outside through lenses, such as general glasses, sunglasses, sportsgoggles or helmets, or a wearable device such as an instrument forexperiencing virtual reality or augmented reality can be included.

A typical application to which the transmittance-variable device of thepresent application can be applied is eyewear. Recently, for sunglasses,sports goggles, instruments for experiencing augmented reality, and thelike, the eyewear in which a lens is mounted so as to be inclined withan observer's front visual line is commercially available. Thetransmittance-variable device of the present application can also beeffectively applied to the above-described eyewear.

When the transmittance-variable device of the present application isapplied to eyewear, the structure of the eyewear is not particularlylimited. That is, the transmittance-variable device may be mounted andapplied in a lens for a left eye and/or a right eye having a knowneyewear structure.

For example, the eyewear may comprise a left eye lens and a right eyelens; and a frame for supporting the left eye lens and the right eyelens.

FIG. 5 is an exemplary schematic diagram of the eyewear, which is aschematic diagram of the eyewear comprising the frame (82), and left eyeand right eye lenses (84), but the structure of the eyewear to which thetransmittance-variable device of the present application can be appliedis not limited to FIG. 5 .

In the eyewear, the left eye lens and the right eye lens may eachcomprise the transmittance-variable device. Such a lens may compriseonly the transmittance-variable device, or may also comprise otherconfigurations.

Other configurations and designs of the eyewear are not particularlylimited, and known methods can be applied.

Advantageous Effects

The present application can provide a transmittance-variable device,which can be applied to various applications without causing problemssuch as a crosstalk phenomenon, a rainbow phenomenon or a mirroringphenomenon, while having excellent transmittance-variablecharacteristics.

BRIEF DESCRIPTION OF DRAWINGS

FIGS. 1 to 4 are schematic diagrams of exemplary transmittance-variabledevices of the present application.

FIG. 5 exemplarily shows eyewear.

FIG. 6 is a diagram schematically showing a method of confirming athickness of a transmittance-variable layer.

FIG. 7 is a transmittance graph obtained in a process of confirming athickness of a transmittance-variable layer.

FIG. 8 is a diagram schematically showing a process of evaluatingrefractive index anisotropy.

FIG. 9 is a view comparing the results of Examples and ComparativeExamples.

MODE FOR INVENTION

Hereinafter, the present application will be specifically described byway of Examples, but the scope of the present application is not limitedby the following examples.

1. Phase Difference Evaluation of Polymer Film

The in-plane retardation value (Rin) of the polymer film was measuredfor light having a wavelength of 550 nm using a UV/VIS spectroscope 8453instrument from Agilent Co., Ltd. Two sheets of polarizers wereinstalled in the UV/VIS spectroscope so that their transmission axeswere orthogonal to each other, and a polymer film was installed betweenthe two sheets of polarizers so that its slow axis formed 45 degreeswith the transmission axes of the two polarizers, respectively, and thenthe transmittance according to wavelengths was measured. The phaseretardation order of each peak is obtained from the transmittance graphaccording to wavelengths. Specifically, a waveform in the transmittancegraph according to wavelengths satisfies Equation A below, and themaximum peak (Tmax) condition in the sine waveform satisfies Equation Bbelow. In the case of λmax in Equation A, since the T of Equation A andthe T of Equation B are the same, the equations are expanded. As theequations are also expanded for n+1, n+2 and n+3, arranged for n and n+1equations to eliminate R, and arranged for n into λn and λn+1 equations,the following Equation C is derived. Since n and λ can be known based onthe fact that T of Equation A and T of Equation B are the same, R foreach of λn, λn+1, λn+2 and λn+3 is obtained. A linear trend line of Rvalues according to wavelengths for 4 points is obtained and the R valuefor the equation 550 nm is calculated. The function of the linear trendline is Y=ax+b, where a and b are constants. The Y value when 550 nm hasbeen substituted for x of the function is the Rin value for light havinga wavelength of 550 nm.

T=sin²[(2πR/k)]  [Equation A]

T=sin²[((2n+1)π/2)]  [Equation B]

n=(λn−3λn+1)/(2λn+1+1−2λn)  [Equation C]

In the above, R denotes in-plane retardation (Rin), a denotes awavelength, and n denotes a nodal degree of a sine waveform.

2. Thickness Evaluation of Transmittance-Variable Layer (Liquid CrystalLayer)

A thickness of a transmittance-variable layer, that is, a cell gap wasmeasured in the following manner using a spectrometer. As shown in FIG.6 , one surface of a transmittance-variable layer having a cell gap d isirradiated with light (I_(I)), and the light (I_(T)) transmitted fromthe other surface is measured. Upon irradiation of the light, theirradiation angle is parallel to the imaginary surface normal directionof the transmittance-variable layer. By checking the transmittance foreach wavelength in this manner, a transmittance graph as shown in FIG. 7may be obtained by constructive interference. The graph obtained asshown in FIG. 7 has a relationship of Equation E below with the cell gap(d), which is the thickness of the transmittance-variable layer, whereinc in Equation E below is the number of peaks present between wavelengthsλ₁ and λ₂ in FIG. 7 . That is, from the graph obtained as shown in FIG.7 , the number of peaks between wavelengths λ₁ and λ₂, which is the κ,can be obtained, and the cell gap (d) can be obtained by substitutingthe wavelengths λ₁ and λ₂ into Equation E.

$\begin{matrix}{d = \frac{\kappa}{2( {{{1/\lambda}1} - {{1/\lambda}2}} )}} & \lbrack {{Equation}E} \rbrack\end{matrix}$

3. Refractive Index Anisotropy Evaluation of Transmittance-VariableLayer (Liquid Crystal Layer)

Refractive index anisotropy (Δn) of a transmittance-variable layer isevaluated in the following manner using an Abbe refractometer. Bycoating a vertical alignment film on the measuring prism andillumination prism surfaces of the Abbe refractometer and coating aliquid crystal compound to be measured on the measuring prism and thencovering it with the illumination prism, the liquid crystal compound isvertically oriented by the vertical orientation force of the twointerfaces. The liquid crystal compound applied in the above process isonly the liquid crystal compound, which is applied to thetransmittance-variable layer, without mixing with other materials suchas dichroic dye.

Then, as shown in FIG. 8 , when a linear polarizer is applied to theeyepiece side and irradiated with light to be observed, θe and θo asshown in FIG. 8 can be obtained and the extraordinary refractive index(n_(e)=n_(p) sin θe) and the ordinary refractive index (n_(o)=n_(p) sinθo) can be obtained through the refractive index (n_(p)) of themeasuring prism and the angles (θe and θo), where the difference(n_(e)−n_(o)) may be defined as the refractive index anisotropy. Thereference wavelength upon measurement is approximately 550 nm.

Example 1

A device was manufactured using a highly stretched PET (polyethyleneterephthalate) film substrate (SRF substrate, thickness: 80 μm,manufacturer: Toyobo, product name: TA044) from Toyobo as s a polymerfilm substrate. An ITO (indium tin oxide) film (electrode layer) wasfirst deposited on one surface of the SRF substrate, and an alignmentfilm was formed. The applied SRF substrate has in-plane retardation ofapproximately 11.000 nm to 14.000 nm based on the wavelength of 550 nmafter the ITO film is deposited. The alignment film was formed byrubbing a polyimide-based horizontal alignment film (SE-7492, Nissan)having a thickness of approximately 300 nm with a rubbing cloth, whereinthe rubbing direction (alignment direction) and the slow axis directionof the SRF substrate were set to approximately 0 degrees (manufacture ofthe upper substrate, the viewer side substrate). The lower substrate wasmanufactured in the same manner. Upon manufacturing the lower substrate,the rubbing direction (alignment direction) and the slow axis directionof the SRF substrate were set to approximately 0 degrees. The uppersubstrate and the lower substrate were disposed so that the respectivealignment films faced (cell gap: 12 μm), and sealed after injecting aliquid crystal material therein to manufacture the device.

Upon the arrangement, the upper substrate and the lower substrate weredisposed so that their alignment directions were parallel to each other,but the rubbing directions were opposite to each other. In addition, asthe liquid crystal material, a composition was used, in which a chiraldopant (S811, Merck) was blended at a concentration of about 0.66 wt %with a liquid crystal compound having positive dielectric constantanisotropy with refractive index anisotropy (Δn) of approximately 0.076(a mixture that a dichroic dye (JD 12, mixed dye of three dyes of cyan,magenta, and yellow colors on a British color synthesis solution) fromLG Chem as the dichroic dye was blended at a concentration ofapproximately 1.8 wt % with SHN-5011XX (JNC)). The obtainedtransmittance-variable layer (liquid crystal layer) is an STN modeliquid crystal layer having a twisted angle of approximately 360degrees.

Example 2

A device was manufactured in the same manner as in Example 1, but thedevice was manufactured such that the alignment direction (rubbingdirection) was approximately 30 degrees clockwise with the slow axis ofthe SRF substrate upon forming the upper and lower substrates. The uppersubstrate and the lower substrate were disposed in the same cell gap asin Example 1 so that the respective alignment films faced, and sealedafter injecting the same liquid crystal material as in Example 1 thereinto manufacture the device. Upon the arrangement, the upper substrate andthe lower substrate were disposed so that their alignment directionswere parallel to each other, but the rubbing directions were opposite toeach other. The obtained transmittance-variable layer (liquid crystallayer) is an STN mode liquid crystal layer having a twisted angle ofapproximately 360 degrees. The applied chiral dopant (S811, Merck) haslevorotation, and thus the angle between the slow axis of the uppersubstrate (SRF substrate) and the alignment direction of the liquidcrystal alignment film measured along the twisting direction of the STNmode is approximately 30 degrees by this arrangement.

Example 3

A device was manufactured in the same manner as in Example 1, but thedevice was manufactured such that the alignment direction (rubbingdirection) was approximately 50 degrees clockwise with the slow axis ofthe SRF substrate upon forming the upper and lower substrates. The uppersubstrate and the lower substrate were disposed in the same cell gap asin Example 1 so that the respective alignment films faced, and sealedafter injecting the same liquid crystal material as in Example 1 thereinto manufacture the device. Upon the arrangement, the upper substrate andthe lower substrate were disposed so that their alignment directionswere parallel to each other, but the rubbing directions were opposite toeach other. The obtained transmittance-variable layer (liquid crystallayer) is an STN mode liquid crystal layer having a twisted angle ofapproximately 360 degrees. The applied chiral dopant (S811, Merck) haslevorotation, and thus the angle between the slow axis of the uppersubstrate (SRF substrate) and the alignment direction of the liquidcrystal alignment film measured along the twisting direction of the STNmode is approximately 50 degrees by this arrangement.

Comparative Example 1

A device was manufactured in the same manner as in Example 1, exceptthat a PC (polycarbonate) film substrate PC substrate, thickness: 100μm, manufacturer: Teijin, product name: PFC100-D150), which was anisotropic film substrate, was applied as a polymer film substrate. Inthis case, since the applied film substrate is an isotropic filmsubstrate, the relationship between the alignment direction of thealignment film and the slow axis of the substrate is not considered.

the following physical properties of the asymmetric substrate accordingto the present application are measurement results in a state where anITO (indium tin oxide) film having a thickness of about 20 nm is formedon one surface of each film substrate.

Test Example

An absorbing linear PVA (polyvinyl alcohol) polarizer was disposed onone surface of the devices manufactured in Examples and ComparativeExamples, respectively, and the change in color coordinates (CIE La*b*)of the emitted light was measured while rotating the absorption axis ofthe polarizer in a range of 0 degrees to 360 degrees. FIG. 9 is themeasurement results as above. It can be confirmed from the drawing thatthe change in color coordinates (a*-b* color coordinate) issignificantly less in the cases of Examples 1 to 3 than in the case ofComparative Example 1.

1. A transmittance-variable device, comprising: a retardation filmhaving in-plane retardation of 5,000 nm or more for light having awavelength of 550 nm; a transmittance-variable layer configured togenerate a polarization component; and first and second liquid alignmentfilms are present on both sides of the transmittance-variable layer,wherein an angle between a slow axis of the retardation film and analignment direction of the first liquid crystal alignment film locatedclose to the retardation film is in a range of 0 degrees to 70 degreeswherein the alignment direction of the first liquid crystal alignmentfilm and the alignment direction of the second liquid crystal alignmentfilm are parallel to each other.
 2. The transmittance-variable deviceaccording to claim 1, wherein a ratio (Tmax/Tmin) of a maximumtransmittance (Tmax) to a minimum transmittance (Tmin) is in a rangefrom 1.5 to
 10. 3. The transmittance-variable device according to claim1, wherein the first liquid crystal alignment film is formed on asurface of the retardation film.
 4. The transmittance-variable deviceaccording to claim 1, further comprising a substrate having a firstsurface on which the first liquid crystal alignment film is formed,wherein the retardation film is attached to a second surface of thesubstrate on which the first liquid crystal alignment film is notformed.
 5. The transmittance-variable device according to claim 1,wherein the transmittance-variable layer is a liquid crystal layerconfigured to form a horizontal orientation mode or an obliqueorientation mode.
 6. The transmittance-variable device according toclaim 5, wherein the horizontal orientation mode and the obliqueorientation mode are twist modes.
 7. The transmittance-variable deviceaccording to claim 1, wherein the transmittance-variable layer is aliquid crystal layer configured to implement a twist orientation mode,and wherein an angle between the slow axis of the retardation film andthe alignment direction of the first liquid crystal alignment filmmeasured along a twisting direction of the twist orientation mode is ina range from 0 degrees to 70 degrees.
 8. The transmittance-variabledevice according to claim 7, wherein the twist orientation mode is ahorizontal twist orientation mode or an oblique twist orientation mode.9. The transmittance-variable device according to claim 5, wherein theliquid crystal layer comprises a dichroic dye.
 10. Thetransmittance-variable device according to claim 7, wherein the liquidcrystal layer comprises a chiral agent.
 11. The transmittance-variabledevice according to claim 1, wherein the liquid crystal layer has athickness of 20 μm or less.
 12. An eyewear, comprising: a left eye lensand a right eye lens; and a frame configured to support the left eyelens and the right eye lens, wherein each of the left eye lens and theright eye lens comprises the transmittance-variable device of claim 1.13. The transmittance-variable device according to claim 7, wherein theliquid crystal layer comprises a dichroic dye.
 14. Thetransmittance-variable device according to claim 1, the retardation filmhas the in-plane retardation between 5000 nm and 50,000 nm.
 15. Thetransmittance-variable device according to claim 1, wherein the liquidcrystal layer has a thickness between 0.01 um to 20 um.